There are articulated tracked vehicles which have a front and a rear vehicle portion which are linked together controllably by means of a control gear. The vehicle comprises one or more drive motors, which, via a transmission, distribute the power to the respective track of the vehicle. The output shafts from the transmission drive the drive shafts of the front and rear vehicle portions at an equally high rotation speed.
EP-A1-0424345 shows an articulated vehicle and a method for facilitating the propulsion of an articulated vehicle. When the driver is positioned in the front vehicle portion, the driver has difficulty in monitoring the movements of the rear vehicle portion, especially when the vehicle is turning. By providing the vehicle with a differential transmission, a greater drive power can be distributed to the front vehicle portion compared with the rear vehicle portion, which means that the rear vehicle will follow the motional direction of the front vehicle portion.
When articulated tracked vehicles of the above-stated type are propelled on a soft ground surface, such as snow or boggy ground, the drive power of the respective vehicle portion is determined by the maximally available drive power which the tracks can produce against the ground minus the oppositely directed driving resistance forces. The drive power which the tracks can produce is generated, inter alia, by the relationship between track slip and sinking of the tracks into the ground surface. This relationship is different for different ground surfaces and different vehicle configurations, such as track configuration and vehicle weight.
When an articulated tracked vehicle travels on a soft ground surface, the track of the rear vehicle portion will travel on a surface compacted by the track of the front car. If the front and rear tracks of the tracked vehicle rotate at the same speed, which is customary in conventionally constructed articulated tracked vehicles, the front and rear tracks will operate with a slip which is not optimal with respect to the efficiency and drive power of the vehicle, for either the front or rear vehicle portion.
When known articulated tracked vehicles turn, a similar drawback occurs. Where the control gear between the front and rear vehicle portion is designed such that the control point is displaced forward, the rear vehicle portion will travel with a smaller radius than the front vehicle portion in the course of a turn. In a turn, the rear vehicle portion thus pushes against the front vehicle portion, since the driveline, in the case of conventionally designed drivelines, is rigidly coupled and the axle transmissions and tracks of both vehicle portions are forced to rotate at the same speed. This means that the tracks have a tendency to lose grip against the surface when the vehicle is turning on slippery or soft ground surfaces. At the same time, the stress on the tracks is high, which means increased wear on the tracks and on the driveline, and increased rolling resistance of the tracks.